Communication systems

ABSTRACT

A communication system for the mutual interconnection of a plurality of lower traffic level (5 Terabit) switch nodes via a relatively higher traffic level (Petabit) connection bus, which system comprises in operative association with each node, a two part TDM optical data management interface, wherein a first of the two parts comprises a time slot resequencer which serves to provide for the transmission of data from its associated node to the bus, and wherein a second of the two parts comprises a time slot specific combiner which serves for the transmission of data from the bus to its associated node, each node and the bus having independent data scheduling.

[0001] The present invention relates to communication systems. More particularly but not exclusively it relates to such systems which use optical TDM (time division multiplex) switch cores.

[0002] Such switch cores are well known to the cognoscenti and moreover, the operation of an optical backplane and/or apparatus for use therewith is described in our co-pending Patent Application Nos. GB 2353157A, and GB 2362280A, to which attention is hereby directed. Accordingly, neither detailed switch core description nor detailed optical backplane description herein, is believed to be necessary.

[0003] The capacity of the apparatus described in GB2362280A is limited by the throughput of the optical backplane. Typically this is 5 Terabit/s. However in the future, higher capacity switch cores will be required and these can be achieved by the interconnection of a plurality of 5 Terabit/s switch nodes so that any one or more of the ingress ports of any one of such nodes can be selectively connected to the egress port or ports of any other of such nodes via a static Petabit/s optical connection bus, and it is an important object of this invention to provide an optical interconnection system to satisfy this particular requirement. It should however be understood, that the present invention may also find more general application in communication systems.

[0004] According to the present invention, a communication system for the mutual interconnection of a plurality of switch nodes via a connection bus comprises in operative association with each node a two part TDM data management interface, wherein a first of the two parts comprises a time slot resequencer which serves to provide for the transmission of data from its associated node to the bus, and wherein a second of the two parts comprises a time slot specific combiner which serves for the transmission of data from the bus to its associated node, each node and the bus having independent data scheduling, the switch nodes being operational at a lower traffic transmission level than the connection bus.

[0005] The communication system may be a TDM optical system wherein data is transmitted optically between the switch nodes, the interface, and the bus.

[0006] The timeslot resequencer of each interface may comprise an optical splitter fed from its associated switch node and coupled to the bus via a timeslot selector, a time delay device, and an optical combiner which feeds the bus.

[0007] The timeslot-specific combiner of each interface may comprise a time delay device, a timeslot selector and an optical combiner via which its associated switch node is fed from the bus.

[0008] The switch nodes of the system may each comprise ingress ports coupled to the timeslot resequencer of an associated interface, and egress ports coupled via grating means and a time slot selector to the timeslot-specific combiner of this associated interface.

[0009] The interface may be arranged to provide for 5 Terabit/s coupling between the switch nodes and the bus and for Petabit/s coupling between the bus and the switch nodes.

[0010] The switch nodes may each comprise a 128×128 switch fabric.

[0011] One embodiment of the invention will now be described with reference to the accompanying drawing, which is a somewhat schematic block/flow diagram of a switch node interconnection system.

[0012] Referring now to the drawing, a communication system comprises a plurality of 5 Terabit switch nodes, only two of which 1, and 2, are shown in the drawing for simplicity of description. Each of the nodes 1, 2, comprises a 128×128 single node switch fabric. The node 1, includes ingress ports 3, coupled to an output line 4, and egress ports 5, each coupled to an input line 6, via a timeslot selector 7, and an optical grating 8, switch operation being locally controlled by means of a scheduler 9. The other node 2, is substantially identical comprising, ingress ports 10, coupled to an output line 11, and egress ports 12, each coupled to an input line 13, via a time slot selector 14, and an optical grating 15, switch operation being locally controlled by a scheduler 16.

[0013] In order to connect any one or more of the ingress ports 3, of the node 1, via an optical bus arrangement which may be implemented as a crossconnect 17, which has its own scheduling engine 18, to any egress port of any other node, (such as one of the egress port or ports 12, of the node 2, for example), a two level traffic management interface system is provided which comprises for each node a similar Petabit expansion box. In this particular embodiment boxes 19, and 20, for the nodes 1, and 2, respectively are provided.

[0014] The expansion box 19, handles traffic to/from the node 1, and comprises a time slot resequencer 21, which operates on the 5 Terabit level to couple the ingress ports 3, to the crossconnect 17, and a time-slot specific combiner 22, which operates on the Petabit level to couple the crossconnect 17, to the egress ports 5.

[0015] Similarly, the expansion box 20, handles traffic to/from the node 2, and comprises a time slot resequencer 23, which operates on the 5 Terabit level to couple the ingress ports 10, to the crossconnect 17, and a time-slot specific combiner 24, which operates to on the Petabit level to couple the crossconnect 17, to the egress ports 12.

[0016] The time slot resequencer 21, operating on the 5 Terabit level, comprises an optical splitter 25, fed from the line 4, a time slot selector 26, a time delay 27, and an optical combiner 28, coupled to the crossconnect 17, whereas its associated timeslot-specific combiner 22, which operates on the Petabit level, comprises time delay 29, fed from the crossconnect 17, timeslot selector 30, and an optical combiner 31, which is coupled to the line 6, so as in effect to reverse the data expansion process.

[0017] Similarly, the time slot resequencer 23, which operates on the 5 Terabit level, comprises an optical splitter 32, fed from the line 11, a time slot selector 33, a time delay 34, and an optical combiner 35, coupled to the crossconnect 17, whereas its associated timeslot-specific combiner 24, which operates on the Petabit level, comprises time delay 36, fed from the crossconnect 17, a timeslot selector 37, and an optical combiner 38, which is coupled to the line 13.

[0018] It will be appreciated that although only two nodes are shown in this example, several nodes may be similarly interconnected to the crossconnect 17, each via its own Petabit expansion box.

[0019] In operation, the system as just before described utilises algorithms which run at two levels, i.e. the 5 Terabit level of the switch nodes and the Petabit level of the extension system comprising the expansion boxes 19, and 20, and the crossconnect 17, each node being responsible for managing the slot allocation or scheduling of its own backplane. It will pass to the extension system, information concerning traffic destined for other nodes with which it is linked via the extension system. Once the extension system has opened a connection between two nodes, the local node will select which of its ingress ports will transmit to the egress port of the external node and pass that information to the traffic management system of the external node.

[0020] In order to carry information on the ingress nodes backplane, it must be extracted from that backplane, moved in time and inserted into a new slot on an extension backplane. This will carry the traffic to the external node where it will again be extracted, moved in time and inserted into the appropriate slot of the egress nodes back plane. This is in effect an optical time and space switch which is defined in this system by the splitters, couplers and delay lines/devices as shown.

[0021] A system as just before described has the advantage that use of the timeslot resequencers facilitate independent delay for each of the 128 timeslots and moreover, all 128 could be outputted if so required. In operation, the timeslot-specific combiners provide a 128:1 optical switch with 50 Pic/sec switching speed. It will be appreciated that scheduling resolves internal/external time slot contention and that the implementation is inherently scalable in accordance with traffic requirements. 

1. A communication system for the mutual interconnection of a plurality of switch nodes via a connection bus comprising in operative association with each node, a two part TDM data management interface, wherein: a first of the two parts comprises a time slot resequencer which serves to provide for the transmission of data from its associated node to the bus, and wherein a second of the two parts comprises a time slot specific combiner which serves for the transmission of data from the bus to its associated node, each node and the bus having independent data scheduling, the switch nodes being operational at a lower traffic transmission level than the connection bus.
 2. A communication system as claimed in claim 1, wherein the communication system is a TDM optical system, data being transmitted optically between the switch nodes, the interface, and the bus.
 3. A communication system as claimed in any preceding claim, wherein the timeslot resequencer of each interface comprises an optical splitter fed from its associated switch node and coupled to the bus via a timeslot selector, a time delay device, and an optical combiner which feeds the bus.
 4. A communication system as claimed in any preceding claim, wherein the timeslot-specific combiner of each interface comprises a time delay device, a timeslot selector and an optical combiner via which its associated switch node is fed from the bus.
 5. A communication system as claimed in claim 4, wherein the switch nodes of the system each comprise ingress ports coupled to the timeslot resequencer of an associated interface, and egress ports coupled via grating means and a time slot selector to the time slot-specific combiner of this associated interface.
 6. A communication system as claimed in any preceding claim, wherein the interface is arranged to provide for 5 Terabit coupling between the switch nodes and the bus, and for Petabit coupling between the bus and the switch nodes.
 7. A communication system as claimed in any preceding claim, wherein the switch nodes each comprise a 128×128 switch fabric.
 8. A communication system substantially as hereinbefore described with reference to the accompanying drawings. 